The present invention relates to a print control method and print control apparatus for controlling a printer which prints an image on a print medium by using a printhead, and a printer using the same.
Specific examples on density unevenness generated by an ink-jet printer will be described with reference to FIGS. 12A to 12C and FIGS. 13A to 13C, taking a single color ink-jet head 91 as an example.
In FIG. 12A, reference numeral 91 denotes an ink-jet head. To simplify the explanation, the drawing shows a case where the ink-jet head 91 comprises eight nozzles 92. Reference numeral 93 denotes ink droplets discharged by each of the nozzles 92. It is ideal when the ink droplets, each having a uniform discharge amount, are discharged in the same direction as shown in FIG. 12A. If such discharge operation is realized, dots having a uniform size are formed on a print paper as shown in FIG. 12B, achieving an image as shown in FIG. 12C in which there is no density unevenness in the nozzle array direction of the ink-jet head 91.
However, in the ink-jet head 95 (FIG. 13A) used in reality, the shape and ink discharge characteristic of each of the nozzles vary. If the ink-jet head 95 is driven similarly to the case of FIG. 12A to perform printing, the size and direction of ink droplets discharged by each of the nozzles varies as shown in FIG. 13A. Therefore, the dots formed on a print paper by the discharged ink droplets are not uniform as shown in FIG. 13B. More specifically, as can be seen from FIG. 13B, high and low density portions appear periodically in the main-scanning direction of the ink-jet head 95, or plural dots unnecessarily overlap with each other, or a white line (non-printed portion) is generated as shown in the central portion of FIG. 13B. The aggregated dots formed in such condition have the density distribution shown in FIG. 13C, which corresponds to the nozzle array direction of the ink-jet head 95. In this case, density unevenness is clearly visible by human eyes. Moreover, such conspicuous line is attributable not only to the ink-jet head 95 but also to an uneven paper-conveyance amount.
To reduce such density unevenness and a white omission line between adjacent raster lines, Japanese Patent Application Laid-Open (KOKAI) No. 60-107975 proposes the following method adopted to a monochrome ink-jet printer.
The method is now briefly described with reference to FIGS. 14A to 14C and FIGS. 15A to 15C. According to this method, the ink-jet head 95 is scanned three times to print the area shown in FIGS. 12A to 12C or FIGS. 13A to 13C. The area corresponding to four pixels, which is printed by half of the nozzles of the ink-jet head 95, is printed by scanning twice. In other words, the eight nozzles of the ink-jet head 95 are divided into two groups: four nozzles in the upper side and four nozzles in the lower side. In the first scanning operation, the four nozzles in the lower side of the ink-jet head 95 are used to print every other pixels, and in the second scanning operation, the four nozzles in the upper side of the ink-jet head 95 are used to scan the same area and print dots in the portion skipped by the first scanning operation, whereby completing printing of the area of interest. The above-described printing method is called fine printing. Adopting the fine printing method to the ink-jet head 95 shown in FIG. 13A enables to reduce the influence of uneven nozzles over a printed image. Therefore, as shown in FIG. 14B, the printed image does not have conspicuous black lines or white lines which are generated in FIG. 13B. Also in this case, density unevenness is relatively reduced as shown in FIG. 14C, as compared to FIG. 13C.
When performing printing in the foregoing manner, image data is divided so as to complement each other in accordance with a predetermined arrangement in the first and second scanning operations. FIGS. 15A to 15C show the examples of image data arrangement (masked pattern). The image data arrangement in FIGS. 15A to 15C shows a checker pattern in which image data is divided to print every other pixels in the vertical and horizontal directions. Therefore, to complete print operation of a unit area (a unit of four pixels in this case), a checker pattern is printed in the first scanning and a reverse checker pattern is printed in the second scanning operation.
FIGS. 15A to 15C show how the print operation of a predetermined area is completed when a checker mask pattern and a reverse checker mask pattern are alternatively used, by utilizing an ink-jet head having eight nozzles similarly to the case of FIGS. 12A to 12C-14A to 14C.
In the first scanning operation, the checker pattern is printed by using the four nozzles in the lower side of the ink-jet head (FIG. 15A). In the second scanning operation, the print paper is conveyed for a distance corresponding to four pixels and the reverse checker pattern is printed by using all the nozzles of the ink-jet head (FIG. 15B). Note that in FIGS. 15A to 15C, the dots (circles) indicated by hatching represent the dots printed by the checker pattern (FIGS. 15A and 15C), while the dots without hatching represent the dots printed by the reverse checker pattern (FIG. 15B). Further in the third scanning operation, the print paper is conveyed again for a distance corresponding to four pixels (xc2xd of all nozzles) and the checker pattern is printed again by using the four nozzles in the upper side of the ink-jet head (FIG. 15C). By alternately performing the sequential paper conveyance in units of four pixels and the printing operation of a checker pattern or a reverse checker pattern as described above, printing an area in units of four pixels is completed per one scanning.
In a case of performing printing by the aforementioned multi-scanning, various mask patterns are used to remove pixel data in each scanning operation. Examples thereof are the aforementioned checker pattern and reverse checker pattern type, horizontal-line type, vertical-line type, or a type where the mask pattern (image-correspondence type mask) changes in accordance with image data and so forth. The image-correspondence type mask is a pattern in which printing orders are predetermined in raster units. For example, assuming a case of performing printing by scanning twice, in the first scan, the first dot of the first raster line is printed (shown as white circle in FIG. 16); the second dot of the first raster line is not: printed (shown as black circle in FIG. 16); and this is repeated for the third and subsequent dots of the first raster line. Then, the first dot of the second raster line is not printed (shown as black circle in FIG. 16); the second dot of the second raster line is printed (white circle in FIG. 16); and this is repeated for the third and subsequent dots of the second raster line. The arrangement of dots to be printed in the first scan (pass) is determined in this manner.
Next, in the second scan, the first dot of the first raster line is not printed (shown as white circle in FIG. 16); the second dot of the first raster line is printed (black circle in FIG. 16); and this is repeated for the third and subsequent dots of the first raster line. Then, the first dot of the second raster line is printed (black circle in FIG. 16); the second dot of the second raster line is not printed (white circle in FIG. 16); and this is repeated for the third and subsequent dots of the second raster line.
By setting the arrangement of dots to be printed in each raster, the checker mask pattern and reverse checker mask pattern are printed as shown in FIG. 16. The mask data used in this case is determined in accordance with, for instance, the image shown in FIG. 17. FIG. 17 shows an image in which only the first dot of the second raster is apart from other dots. In the image in FIG. 17, dots of the second raster are printed from the first dot in the order of xe2x80x9cnot printxe2x80x9d, xe2x80x9cprintxe2x80x9d . . . , in the first scan. As can be seen in FIG. 17, printed dots of the first raster through the third raster create a vertical-consecutive pattern (vertical line). Herein, note that white dots in FIG. 17 represent dots printed in the first scanning operation and black dots represent dots printed in the second scanning operation.
FIG. 17 shows an example in which the aforementioned vertical-line pattern is created by using mask data for thinning. The image data, which has been thinned out by the foregoing mask pattern, causes to generate the portion where printed dots are consecutive along the column of the mask pattern (three printed dots are vertically consecutive in FIG. 17). In such portion where printed dots are consecutive, ink droplets may merge on the surface of the print medium if the ink permeating speed on the print medium is slow. Such phenomenon is called beading. Such vertical lines generated as described above are factors of image deterioration, thus being problematic.
The present invention has been made in consideration of the above situation, and has as its object to provide a print control method and apparatus, as well as a printer, for reducing image deterioration caused by printed dots that are consecutive, by decreasing the density value of image data having high density.
Another object of the present invention is to provide a print control method and apparatus, as well as a printer, for preventing printed dots that are consecutive, by removing bits from a mask pattern used for thinning out print data, to reduce image deterioration.
Another object of the present invention is to provide a print control method and apparatus, as well as a printer, for preventing printed dots that are consecutive, by changing a mask pattern in accordance with the type of ink used in the print operation, to reduce image deterioration.
Another object of the present invention is to provide a print control method and apparatus, as well as a printer, for preventing image deterioration caused by printed dots that are consecutive on a print medium, by changing a mask pattern in accordance with the type of print medium used in the print operation.
Still another object of the present invention is to provide a print control method and apparatus, as well as a printer, for preventing image deterioration caused by printed dots that are consecutive on a print medium, by changing a mask pattern in accordance with the resolution of the print data used in the print operation.
Another object of the present invention is to provide a print control method and apparatus, as well as a printer, for preventing beading and preventing the missing printable dots from being obvious by reducing the highest density value or the maximum number of printable dots to 97% to 99% of the value or the number.
By reducing the highest density value or the maximum number of printable dots to less than 99% of the value or the number, it is possible to prevent beading, and by reducing the highest density value or the maximum number of printable dots to be between 97% to 99% of the value or the number, it is possible to prevent beading without conspicuous image deterioration caused by removing printable dots.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.